The dry weight of the material may be important in determining the density and moisture content of the material. There are many industries where the density and moisture content of material is an important value. In the asphalt industry, samples of asphalt are cut from a newly paved roadway or area where asphalt has been applied. To obtain the density of these materials, a dry weight must be determined. However, water is often introduced into the asphalt sample during the paving process itself. Also, to cut a sample from an asphalt pavement or for preparing samples of a certain size or shape, wet saws or augers are sometimes used. These introduce extra water into the sample, saturating the sample. Because of the natural water that may be present in the sample and because of water that may be introduced in the sample during the paving process or during the cutting process, it is necessary to dry samples to determine a dry weight, hence to calculate accurate density. Under the current practice, samples are placed in an oven heated to a temperature of 105° to 115° centigrade for a predetermined period of time, usually 16 to 24 hours. The water contained within the sample will be evaporated from the sample by the elevated temperature during this period of time. This will give a dried sample which then may be weighed to determine the dry weight. However, in some applications, the drying time required for this method is a drawback. It does not give an opportunity to take quick corrective action during a construction project, should it be determined that the density of the sample is outside of the parameters assigned the project and sample may be damaged by heat applied during drying period.
In the construction industry, compacted asphalt samples are tested using the ASTM Test D2726, the ASTM Test D6752, and the AASHTO Test T166. These tests require the determination of the density of the materials. This requires that the dry mass of a sample along with a sample volume be determined in order to calculate the density, which is the ratio of the mass to the volume. Moisture may be introduced into the sample by the cutting process or may be naturally present in the sample. Consequently, moisture is eliminated from the sample using the oven method described above or by placing the samples in front of a fan. Both methods require a period of time amounting to hours or, in the fan method, days for completely drying samples. Oven drying at higher temperatures could provide a quicker evaporation of the water from the sample, but ordinarily is not recommended. High temperatures can potentially change the characteristics of the sample and damage the sample for other tests that may be required.
In loose asphalt mixtures, it is important to determine the amount of moisture in the mixture. Excessive water can result in stripping of the asphalt binder film from the aggregate. Stripping can cause premature failure and pot hole creation in asphalt pavements. Currently, samples are taken at a site, placed in a sealed jar or container, weighed before drying, an oven-drying method is used to dry the sample, and then a second weight is taken. This will determine the amount of moisture in the sample. This method is not very practical and could be inaccurate because the sample can gain moisture from the atmosphere during the processing of the sample and during weighing of the sample.
Drying is also important in a variety of other industrial contexts. The moisture content of aggregates themselves oftentimes is measured as part of evaluation. The moisture content in raw material used in paper making process, including wood chips, pulp, and finished paper can be important during the manufacturing process. In the chemical industry, various powders and gels are dried during research and production testing. However, powders and gels cannot be exposed to high temperatures without a risk that the chemical composition of the powder or gel would be altered by the higher temperatures. Consequently, vacuum ovens are frequently used to dry gels or powders, but the drying process is a slow one and can take a long time.
Electronic components used in the electronic industry, including the computer industry, must be dried after washing with a solvent. Mae et al., U.S. Pat. No. 5,755,039 proposes a component dryer. A sealed chamber is used where components that are wet with solvent are placed in a vat with a bottom surface permeable to the solvent. Heated air is drawn into the chamber through an air inlet. A fan or other means is placed at the bottom of the chamber to pull air through an air outlet. The heated air is brought into the chamber by the draw created by the fan, passes through the components, and is pulled into the air outlet for exhaust from the chamber by the fan. The air allowed into the chamber is less than the volume of air removed from the chamber by the fan, hence a negative pressure is created in the chamber below the vat containing the components.
Ito et al., U.S. Pat. No. 4,686,852 discloses a mechanical method for preparing mortar or concrete. Here, a fine aggregate is placed in an enclosed container, a centrifugal force is applied to the container of a predetermined period, the centrifugal force removes a portion of the water deposited on the fine aggregate, which allows appropriate determinations to be made. Kuboyama, U.S. Pat. No. 4,319,408 discloses a general drying apparatus. A partially sealed chamber is evacuated forcibly by a rotary means installed in the chamber. The air pressure within the chamber is reduced. A certain amount of air is allowed to be introduced into the chamber while maintaining a balanced pressure within the chamber. Air friction heat is generated by continuous rotation of the rotary air evacuator causing an increased air temperature within the chamber.
Chapman et al., U.S. Pat. No. 5,732,478 supplies heated fresh air to a chamber then evacuating the chamber to remove residual moisture. The flow of air is interrupted to the chamber during evacuation. Air knives are used to introduce the warm dry air into the chamber, which also insures entrained ambient air and a turbulent flow around the devices within the chamber which are to be dried. The Chapman device recognizes that interrupting the flow of heated air during evacuation of the chamber vaporizes moisture but cools the device, resulting in a risk of freezing.
Despite this earlier work there is still need for an improved rapid drying method and apparatus for use in industrial applications. It is an object of the invention to reduce the drying time required for samples. It is an object of the invention to do so in a controlled vacuum. It is an object of the invention to do so at a controlled temperature. It is an object of this invention to do so by controlling the time for vacuum and time for temperature applications. This maintains the material integrity of the samples while, at the same time, expediting the drying process. It is an object of the invention to provide a trap for liquids removed from the sample during the drying process.